According to Andre Ward's twitter, it seems that he injured his left hand quite significantly during the 6th round of his fight with Carl Froch. As you may know, since Andre fights in a regular stance, the left hand would be the lead hand responsible for jabs and the mean left hook he employed during the fight. I would need to see the fight again, but I think that Andre started going back and forth between southpaw and regular stances during the 7th round and this injury may explain why. He wanted to shield the left hand yet still keep a high punch output.
If you look at the CompuBox numbers, it seems that Ward's jab percentage drops significantly from the 6th to the 7th round. Before and including the 6th round Ward was landing his jab at a 50-60% rate, whereas after the 6th round he was landing at a 17-40% rate. This could be due to Ward missing on purpose or the switch to a slightly unnatural southpaw position, but it sure does seem like Ward's jab became less accurate after the 6th round.
On to the injury itself, Andre just announced that the MRI revealed multiple fractures in the third and fifth metacarpal. Apparently this was an aggravation of a previous injury sustained in training a week before the fight. Initial X-Rays revealed that there was no damage so the fight went forward. The fracture on the fifth metacarpal (lowest bone on the pinky finger) is actually somewhat worrying. This specific fracture is named the "boxer's fracture" and is the most common bone to be injured while throwing a punch. The worst part is that once this bone has been broken or fractured, there a high likelihood that it will become fractured again unless great care is taken. This type of problem showing up relatively early in Ward's career signals that he will probably have chronic hand problems unless he gets a hand specialist like Floyd Mayweather Jr.
You really have to applaud Ward for hiding the injury quite effectively and for continuing to both use and put power behind his left hand. Hitting Froch probably hurt Ward as much as it hurt Froch.